#include <stdint.h>
/*
 * Pre-calculated 256-way 1 byte column parity
 */
static const uint8_t nand_ecc_precalc_table[] = {
        0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00,
        0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
        0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
        0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
        0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
        0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
        0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
        0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
        0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
        0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
        0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
        0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
        0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
        0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
        0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
        0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00
};


int nand_calculate_ecc(const uint8_t *dat, uint8_t *ecc_code)
{
        uint8_t idx, reg1, reg2, reg3, tmp1, tmp2;
        int i;

        /* Initialize variables */
        reg1 = reg2 = reg3 = 0;

        /* Build up column parity */
        for(i = 0; i < 256; i++) {
                /* Get CP0 - CP5 from table */
                idx = nand_ecc_precalc_table[*dat++];
                reg1 ^= (idx & 0x3f);

                /* All bit XOR = 1 ? */
                if (idx & 0x40) {
                        reg3 ^= (uint8_t) i;
                        reg2 ^= ~((uint8_t) i);
                }
        }

        /* Create non-inverted ECC code from line parity */
        tmp1  = (reg3 & 0x80) >> 0; /* B7 -> B7 */
        tmp1 |= (reg2 & 0x80) >> 1; /* B7 -> B6 */
        tmp1 |= (reg3 & 0x40) >> 1; /* B6 -> B5 */
        tmp1 |= (reg2 & 0x40) >> 2; /* B6 -> B4 */
        tmp1 |= (reg3 & 0x20) >> 2; /* B5 -> B3 */
        tmp1 |= (reg2 & 0x20) >> 3; /* B5 -> B2 */
        tmp1 |= (reg3 & 0x10) >> 3; /* B4 -> B1 */
        tmp1 |= (reg2 & 0x10) >> 4; /* B4 -> B0 */

        tmp2  = (reg3 & 0x08) << 4; /* B3 -> B7 */
        tmp2 |= (reg2 & 0x08) << 3; /* B3 -> B6 */
        tmp2 |= (reg3 & 0x04) << 3; /* B2 -> B5 */
        tmp2 |= (reg2 & 0x04) << 2; /* B2 -> B4 */
        tmp2 |= (reg3 & 0x02) << 2; /* B1 -> B3 */
        tmp2 |= (reg2 & 0x02) << 1; /* B1 -> B2 */
        tmp2 |= (reg3 & 0x01) << 1; /* B0 -> B1 */
        tmp2 |= (reg2 & 0x01) << 0; /* B7 -> B0 */

        /* Calculate final ECC code */
        ecc_code[0] = ~tmp1;
        ecc_code[1] = ~tmp2;
        ecc_code[2] = ((~reg1) << 2) | 0x03;

        return 0;
}

static inline int countbits(unsigned int byte)
{
        int res = 0;
        for (;byte; byte >>= 1)
                res += byte & 0x01;
        return res;
}


int nand_correct_data(uint8_t *dat, uint8_t *read_ecc, uint8_t *calc_ecc)
{
        uint8_t s0, s1, s2;

        s1 = calc_ecc[0] ^ read_ecc[0];
        s0 = calc_ecc[1] ^ read_ecc[1];
        s2 = calc_ecc[2] ^ read_ecc[2];

        if ((s0 | s1 | s2) == 0)
                return 0;

        /* Check for a single bit error */
        if( ((s0 ^ (s0 >> 1)) & 0x55) == 0x55 &&
            ((s1 ^ (s1 >> 1)) & 0x55) == 0x55 &&
            ((s2 ^ (s2 >> 1)) & 0x54) == 0x54) {

                unsigned int byteoffs, bitnum;

                byteoffs = (s1 << 0) & 0x80;
                byteoffs |= (s1 << 1) & 0x40;
                byteoffs |= (s1 << 2) & 0x20;
                byteoffs |= (s1 << 3) & 0x10;

                byteoffs |= (s0 >> 4) & 0x08;
                byteoffs |= (s0 >> 3) & 0x04;
                byteoffs |= (s0 >> 2) & 0x02;
                byteoffs |= (s0 >> 1) & 0x01;

                bitnum = (s2 >> 5) & 0x04;
                bitnum |= (s2 >> 4) & 0x02;
                bitnum |= (s2 >> 3) & 0x01;

                dat[byteoffs] ^= (1 << bitnum);

                return 1;
        }

        if(countbits(s0 | ((unsigned int)s1 << 8) | ((unsigned int)s2 <<16)) == 1)
                return 1;

        return -1;
}

